Often referred to as the "trust hormone," oxytocin is typically associated with helping couples establish a greater sense of intimacy and attachment. Lesser known, however, is its potential role, if any, in preventing couples from cheating. But as a new study from the University of Bonn suggests, it may in fact prevent committed men from getting too close to other women they find attractive — an indication of just how important the hormone is in promoting fidelity within monogamous relationships.

Oxytocin has a number of things going for it. In addition to creating a sense of trust, it can alleviate social fears, facilitate healing, reduce stress and depression, and even increase generosity. What's unclear, however, is whether the hormone can prevent committed people from getting too friendly with strangers.

Though often referred to as the "trust hormone" oxytocin is increasingly being seen as a…
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In an effort to find out, René Hurle­mann and his colleagues conducted an experiment — and what they discovered was that men in monogamous relationships who were given oxytocin kept a greater distance from women they found attractive, and that this effect held true regardless of whether the men were approaching or being approached by the women.

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To reach this conclusion, Hurle­mann set up an experiment in which a group of healthy heterosexual males were administered oxytocin or a placebo via a nasal spray. About an hour later they were introduced to an attractive female experimenter. During the course of the experiment, the attractive woman regularly altered her distance from the men, while the men were asked to indicate when the experimenter was either at an "ideal distance" or at a distance that made them feel "slightly uncomfortable."

Interestingly, going into the experiment Hurle­mann's team predicted that the men, because they had just been administered oxytocin, would be more comfortable as the woman came closer; it is the "trust hormone" after all. But surprisingly, the exact opposite happened. The researchers observed that the men in committed relationships (but not those who were single) kept a greater physical distance between themselves and the woman.

This effect held true whether or not the woman maintained eye contact or averted her gaze, or if the men were the ones doing the approaching and withdrawing. The oxytocin did not affect the men's attitude toward the female experimenter, who was rated as attractive in all scenarios (placebo included).

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And importantly, committed men who were given the placebo did not insist on the same distance as those administered oxytocin, an indication that the hormone discourages partnered — but not single men — from getting too close to a female stranger.